LT3476 High Current Quad Output Driver DESCRIPTIO LT®3476 quad ou

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LT3476 High Current Quad Output Driver DESCRIPTIO LT®3476 quad ou

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LT3476 High Current Quad Output Driver DESCRIPTIO
LT®3476 quad output DC/DC converter designed operate constant-current source driving high current LEDs. fixed frequency, current mode architecture results stable operation over wide range supply output voltages. frequency adjust allows user program switching frequency between 200kHz 2MHz optimize efficiency external component size. LT3476 senses output current high side LED. High side current sensing most flexible scheme driving LEDs, allowing buck, boost buckboost configurations. Each current monitor threshold trimmed within 2.5% full scale 105mV. With external sense resistor, user programs output current range each channel. Each four regulators independently operated that channel's signal. This feature allows precise adjustment color mixing dimming ratio source. Dimming ratios 1000:1 achieved.
Lare registered trademarks Linear Technology Corporation. True Color trademark Linear Technology Corporation. other trademarks property their respective owners.
True Color PWMDimming Delivers 1000:1 Dimming Ratio Current Regulation with High-Side Sense VADJ Accurately Sets Current Sense Threshold Over Range 10mV 120mV Four Independent Driver Channels with 1.5A, Internal Switches Frequency Adjust Pin: 200kHz 2MHz High Efficiency Conversion Open Protection Quiescent Current 22mA Active Mode <10µA Shutdown Mode Wide Range: 2.8V Thermally Enhanced, 38-Lead, Package
APPLICATIO
RGGB Lighting Automotive Avionic Lighting Backlighting Constant-Current Sources
TYPICAL APPLICATIO
PVIN CAP1 100m LED1
100W Quad Driver
CAP2 100m LED2 CAP3 100m LED3 CAP4 100m LED4 2.2µF
LEDS
0.22µF 0.22µF
0.22µF 0.22µF
10µH
10µH
10µH
10µH
ILED 500mA/DIV
1.05V 2.8V PWM1-4 SHDN 2.2µF CAP1-4 LED1-4 PWM1-4 SHDN LT3476 VADJ1-4 VC1-4
3476 TA01
100k 4.7k 22nF
100:1 Dimming 120Hz
LEDs PVIN
3476 TA02
10µs/DIV
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LT3476 ABSOLUTE
(Note
RATI
PACKAGE/ORDER ATIO
VIEW VADJ1 VADJ2 PWM1 PWM2
.16V PWM(1-4), SHDN .16V SW(1-4), LED(1-4), CAP(1-4) .36V REF, VADJ(1-4), VC(1-4) Operating Temperature Range (Note -40°C 85°C Maximum Junction Temperature 125°C Storage Temperature Range. -65°C 125°C Lead Temperature 300°C
LED1 CAP1 CAP2 LED2 LED3 CAP3 CAP4 LED4 PWM4 PWM3 VADJ4 VADJ3 SHDN
PACKAGE 38-LEAD (5mm 7mm) PLASTIC TJMAX 125°C, 34°C/W EXPOSED (PIN (MUST SOLDERED PCB)
ORDER PART NUMBER LT3476EUHF
PART MARKING 3476
Order Options Tape Reel: Lead Free: #PBF Lead Free Tape Reel: #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult Marketing parts specified with wider operating temperature ranges.
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C. unless otherwise noted (Note 3.3V, SHDN 3.3V, GND, PWMn 3.3V, VADJn REF, Open, CAPn
PARAMETER Operating Range Full-Scale Current Monitor Threshold One-Tenth Scale Current Monitor Threshold SWn/CAPn/LEDn Operating Range Output Voltage Line Regulation Quiescent Current Shutdown 10µA IREF -200µA 2.8V SHDN
ELECTRICAL CHARACTERISTICS
CONDITIONS Over CAPn/LEDn Operating Range
1.032
1.050 0.003
1.063
UNITS
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VADJn 100mV
LT3476
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C. unless otherwise noted (Note 3.3V, SHDN 3.3V, GND, PWMn 3.3V, VADJn REF, Open, CAPn
PARAMETER Quiescent Current Idle Quiescent Current Active (Not Switching) Switching Frequency CONDITIONS PWM(1-4) VC(1-4) 8.25k 140k 8.25k (2MHz) (1MHz) 140k (200kHz) Current PWMn 1700 2000 1000 1.26 Static Test 1.3A SHDN 33.5 PWMn 0.4V, 2300 1150 UNITS
ELECTRICAL CHARACTERISTICS
Nominal Voltage Maximum Duty Cycle
VADJn Input Bias Current Idle Input Bias Current EAMP (IVC/VCAP-LED) Output Impedance Current Limit VCESAT Leakage Current CAPn Overvoltage Protect Threshold CAPn/LEDn Idle Input Bias Current CAPn/LEDn Input Bias Current SHDN Input Voltage SHDN Input High Voltage SHDN Current PWM1, PWM2, PWM3, PWM4 Input Voltage PWM1, PWM2, PWM3, PWM4 Input High Voltage PWM1, PWM2, PWM3, PWM4 Current
Note Stresses beyond those listed under Absolute Maximum Ratings cause permanent damage device. Exposure Absolute Maximum Rating condition extended periods affect device reliability lifetime. Note This includes overtemperature protection that intended protect device during momentary overload conditions. Junction temperature will exceed 125°C when overtemperature protection active. Continuous operation above specified maximum operating junction temperature impair device reliability.
Note LT3476E guaranteed meet specifications from 85°C. Specifications over -40°C 85°C operating temperature range assured design, characterization correlation with statistical process controls.
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LT3476 TYPICAL PERFOR CHARACTERISTICS
V(CAP-LED) Threshold VADJ
25°C TYPICAL V(CAP-LED) THRESHOLD (mV) CURRENT LIMIT MINIMUM FOSC (kHz) 1000
VADJ
3476
V(CAP-LED) Threshold Temperature, VADJ VREF
CURRENT LIMIT
OSCILLATOR FREQUENCY (kHz)
V(CAP-LED) THRESHOLD (mV)
TEMPERATURE (°C)
Reference Voltage
1.065
1.060
V(CAP-LED) THRESHOLD (mV)
INPUT CURRENT (mA)
VREF
1.055
1.050
1.045
1.040
TEMPERATURE (°C)
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25°C, unless otherwise noted.
Current Limit Duty Cycle
10000
Oscillator Frequency
DUTY CYCLE
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1000
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Switch Current Limit Temperature
1150 1100 1050 1000
Oscillator Frequency Temperature
TEMPERATURE (°C)
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TEMPERATURE (°C)
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3476
V(CAP-LED) Threshold V(CAP)
VADJ 1.05V
Quiescent Current
3.6V
GND, SWITCHING 25°C
VCAP
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LT3476 CTIO
(Pins 38): Error Amplifier Compensation Pin. When low, floats external compensation capacitor save state next cycle. LEDn (Pins 11): Non-Inverting Input Current Sense Error Amplifier. Connect directly current sense resistor terminal. Switcher will regulate this node voltage VADJ below node. Also connected node through external sense resistor anode string. allow this float independently corresponding input pin. applications where current PVIN changes widely, connect output filter capacitor LEDn. CAPn (Pins 10): Inverting input current sense error amplifier. Connect directly other terminal current sense resistor. Also connected output filter capacitor cathode external Schottky rectifier. greater than overvoltage protect threshold will inhibit switching. (Pin Oscillator Programming Pin. Place resistor connected program oscillator frequency. REF: (Pin Reference Output Pin. Connect VADJ full-scale current. Connect resistor dividers program VADJ pins values lower than 1.05V. Bypass local with 0.1µF capacitor. VADJn (Pins 37): Current Adjustment Pin. Sets voltage across external sense resistor between CAPn LEDn. Connect directly full-scale threshold 105mV, signal vales between modulate current. VADJ input range 1.25V maximum. PWMn (Pins 35): Signal turns channel-disables main switch, reduces quiescent supply current channel, causes channel become high impedance. SHDN (Pin 18): Shutdown Pin. Higher than 1.5V turns device (Pins 32): Used. Connect (Pin better heat dissipation. (Pins 29): Switch Pin. Connect external inductor anode external Schottky rectifier. Minimize area trace plane reduce EMI. (Pin 33): Input Supply Pin. Must locally bypassed. (Pin 39): Signal Power GND. Solder Exposed directly ground plane. Exposed metal package provides both electrical contract ground good thermal contact printed circuit board. must soldered circuit board proper operation.
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LT3476 BLOCK DIAGRA
PVIN
VADJ
1.25V
IDLE MODE
RSET1
RAMP GENERATOR
ISRC 300µA
200kHz 2MHz OSCILLATOR
1.05V
OPERATIO
LT3476 constant-frequency, current mode regulator with internal power switch. Operation best understood referring Block Diagram. start each oscillator cycle, latch set, which turns power switch. voltage proportional switch current added stabilizing ramp resulting into positive terminal comparator, When this voltage exceeds level negative input latch reset, turning power switch. level negative input error amplifier simply amplified version difference between voltage across internal resistor RSET voltage across external current sense resistor RSNS. this manner, error amplifier sets correct peak switch current level regulate current through RSNS. error amplifier's output increases, more current delivered output; decreases, less current delivered.
RSNS (EXT) EXTERNAL COMPONENTS BUCK MODE CBYP 2.2µF CFILT 0.1µF 10µH 22-29 ARRAY
RSET
OVERVOLTAGE DETECT DRIVER COMPARATOR MAIN SWITCH
ERROR AMPLIFIER
THERMAL LIMIT 145°C
0.02
CURRENT SENSE AMPLIFIER
LT3476 CHANNEL
SHUTDOWN SHDN
3476
current regulated RSNS adjusted changing voltage across RSET using VADJ input pin. amplifier regulates current produce voltage across RSET equal VADJ. This current flowing through transistor also produces voltage across RSET onetenth magnitude VADJ input level shifted input. voltage across RSET limited 125mV (typ) separate 1.25V input average current regulated RSNS also adjusted dimming using pin. When low, switching disabled error amplifier turned that does drive pin. Also, internal loads disabled that charge state will saved external compensation capacitor. This feature reduces transient recovery time because when input again transitions high, demand current switch returns value just before last transitioned low.
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LT3476 APPLICATIONS INFORMATION
Layout Hints high speed operation LT3476 demands careful attention board layout. Several items worthy note. exposed package only terminal also important thermal management crucial achieve good electrical thermal contact between exposed ground plane board. Also, Schottky rectifier capacitor between cathode Schottky high frequency switching path where current flow discontinuous. These elements should placed minimize path between reduce EMI, important minimize area trace. plane under minimize interplane coupling sensitive signals. obtain good current regulation accuracy eliminate sources channel-to-channel coupling, inputs each channel LT3476 should separate lines back terminals appropriate sense resistor. Since there small input bias current (~50µA) inputs, resistance series with these inputs should matched, otherwise there will offset. Finally, bypass capacitor supply LT3476 should placed close possible terminal device. Open-Circuit Protection/Overvoltage Lockout LT3476 independent internal overvoltage/opencircuit protection (OVP) four converters, sensed through their respective inputs. purpose feature protect main switch device from damage. boost configuration, LEDs disconnected from circuit fail open, converter output voltage clamped voltage (typ). Figure shows transient response step-up converter application with LED1 disconnected. With LED1 disconnected, converter switches current limit output ramps OVP. Upon reaching clamp voltage, converter will switch with reduced current limit regulate converter output voltage clamp. buck mode application shown Figure should external supply exceed clamp, then switching will inhibited converter. order overvoltage protection feature adequately protect switch, important that input sample voltage near highest voltage reached node. result, this function will provide adequate protection from open load events isolated power configurations such flyback, since input output voltage magnitudes must summed obtain voltage seen switch.
V(CAP) DISCONNECT HERE
I(SW) 1A/DIV 20µs/DIV
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Figure Disconnect Transient
Setting Switching Frequency switching frequency LT3476 external resistor connected between GND. leave this open. Also, load this with capacitor. resistor must always connected proper operation. Table below Oscillator Frequency graph Typical Performance Characteristics resistor values corresponding switching frequencies.
Table Switching Frequency
SWITCHING FREQUENCY (kHz) 1000 1200 2000 61.9 16.2 8.25
general, lower switching frequency should used where either very high very switch duty cycle operation required, higher efficiency desired. Selection higher switching frequency will allow smaller value external components yield smaller solution size profile. Also high frequency dimming, higher switching frequency (shorter switching period)
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LT3476 APPLICATIO ATIO
will give better dimming control since turning switch, state sampled only during narrow time slot beginning each switch period. Inductor Selection inductors used with LT3476 should have saturation current rating 2.5A greater. best loop stability results, inductor value selected should provide ripple current 350mA more. buck (step-down) boost (step-up) configurations, using resistor (TSW 1µs), inductor values from 4.7µH 10µH recommended most applications. buck mode, inductor value estimated using formula: DBUCK DBUCK VCAP VLED VCAP
VLED voltage across string VCAP input voltage converter. boost mode, inductor value estimated using formula: DBOOST DBOOST VCAP
input voltage VCAP voltage across string. Table below provides some suggested components vendors.
Table Inductors
PART NUMBER Sumida CDRH6D38-100 CDRH5D28-5R3 CDRH73-100 Toko D63CB D63CB Cooper-ET SD25-4R7 1.80 0.047 1.49 2.08 0.042 0.026 1.90 1.68 0.028 0.028 0.072 VALUE (µH) IRMS HEIGHT (mm)
Input Capacitor Selection proper operation, necessary place bypass capacitor close LT3476. 1µF, greater, capacitor with should used. ceramic capacitor usually best choice. buck configuration, capacitor input power converter large pulsed currents current returned through Schottky diode when switch off. best reliability, this capacitor should have meet ripple current requirement, IRMS
((1-
where switch duty cycle. 2.2µF ceramic type capacitor placed close Schottky ground plane usually sufficient each channel. Output Capacitor Selection selection output filter capacitor depends load converter configuration, i.e., step-up step-down. applications, equivalent resistance typically low, output filter capacitor should sized attenuate current ripple from inductor 35mA less. following equation useful estimate required capacitor value: CFILT RLED typical filter capacitor value RLED 0.47µF. loop stability, consider output pole frequency where closed loop gain should unity, dominant pole loop compensation will established capacitor input. boost applications, achieve same ripple current required filter capacitor value about five times larger than value calculated above pulsed nature source current. 2.2µF ceramic type capacitor placed close Schottky ground plane usually sufficient each channel. output capacitor subject high ripple current, ceramic capacitors recommended their high frequency.
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LT3476 APPLICATIO ATIO
Ceramic type capacitors using dielectric best temperature bias stability capacitor value. ceramic capacitors exhibit loss capacitance value with increasing voltage bias, necessary choose higher value capacitor larger case size required capacitance operating voltage. Always check that voltage rating capacitor sufficient. Table shows some recommended capacitor vendors.
Table Low-ESR Surface Mount Capacitors
VENDOR Taiyo-Yuden Murata TYPE Ceramic Ceramic Ceramic SERIES X5R, X5R, X5R,
Compensation Design LT3476 uses internal transconductance error amplifier whose output compensates control loop. external inductor, output capacitor, compensation resistor capacitor determine loop stability. inductor output capacitor chosen based performance, size cost. compensation resistor capacitor selected optimize control loop stability. component values shown typical applications circuits yield stable operation over given range input-to-output voltages load currents. most buck applications, small filter capacitor (1µF less) across load desirable. this case, 10nF compensation capacitor usually quite adequate. compensation resistor placed between output compensation capacitor minimizes channel-to-channel interaction reducing transient recovery time. boost configuration will have larger output capacitor, 2.2µF 10µF. following circuit techniques involving compensation helpful where there large variation programmed current, large input supply range expected. duty cycles (TON less than 350ns) average inductor current (less than 500mA), LT3476 start skip switching pulses maintain output regulation. Pulse-skipping mode usually less desirable because leads increased ripple current LED. improve onset pulse-skipping behavior, place capacitor between node compensation
capacitor that 1:1000 value compensation capacitor. buck configuration, additional technique available. filter capacitor between node bottom (see Typical Application first page) moved between bottom. This circuit change places inductor ripple current through sense resistor, which improves pulse-skipping behavior. There usually less than impact current regulation point. Diode Selection Schottky rectifier conducts current during interval when switch turned off. Select diode with rated maximum voltage. boost circuits that output disconnect feature, diode should rated least 40V. necessary that forward current rating diode equal switch current limit. average current through diode function switch duty cycle, select diode with forward current rating 1.5A (1-D). using feature dimming, also important consider diode leakage from output (especially hot) during interval. Table some recommended component vendors.
Table Schottky Diodes
PART NUMBER Semiconductor MBRM140 Diodes Inc. DFLS140L B140 Philips Semiconductor PMEG4010EJ IAVE (mV)
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LT3476 APPLICATIO ATIO
Programming Current Current programmed using external sense resistor series with load. This method allows flexibility driving load (i.e., sensing several parallel strings) while maintaining good accuracy. VADJ input sets voltage regulation threshold across external sense resistor between 10mV 120mV. 1.05V reference output (REF) provided drive VADJ pins either through resistor divider, connected directly give full-scale current 105mV. also used drive VADJ pins. VADJ pins should left open. VADJ input connected voltage higher than 1.25V, default regulation threshold across 125mV (typ). VADJ also used conjunction with thermistor provide overtemperature protection load.
VREF 1.05V VADJ1-4
3476
Figure Overtemperature Protect Circuit
Dimming Control There methods control current source dimming using LT3476. first method, popular with applications, uses modulate current source between zero full current achieve precisely programmed average current. make this method current control more accurate, during quiescent phase switch demand current stored node. This feature minimizes recovery time when signal goes high. minimum off-time will depend choice operating frequency through input pin. best current accuracy, minimum high time should least switching cycles. This guideline reasons: first allow output reach steady state before shutting off, second because oscillator synchronized signal there much switching cycle delay from going high start switching. This delay, however, does apply negative transition signal. minimum low/high time reduced five switching cycles disconnect switch used current path. second method dimming control uses VADJ linearly adjust current sense threshold during high state. current programming feature augments dimming control, possibly increasing total dimming range factor ten.
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LT3476 TYPICAL APPLICATIO
PVIN 350mA 350mA 10µH LED1 300m LED2 300m 10µH 350mA 10µH LED3 300m 350mA 10µH LED4 300m
Step-Up/Step-Down Driver Series 350mA LEDs
CAP1 2.2µF
2.8V
PWM1-4 SHDN 2.2µF
PACKAGE DESCRIPTIO
0.70 0.05 5.50 0.05 SIDES) 4.10 0.05 SIDES) 3.15 0.05 SIDES) MARK (SEE NOTE
PACKAGE OUTLINE 0.25 0.05 0.50 5.15 0.05 SIDES) 6.10 0.05 SIDES) 7.50 0.05 SIDES) RECOMMENDED SOLDER LAYOUT 0.75 0.05 0.200 0.200 0.00 0.05
Information furnished Linear Technology Corporation believed accurate reliable. However, responsibility assumed use. Linear Technology Corporation makes representation that interconnection circuits described herein will infringe existing patent rights.
CAP2 2.2µF 2.2µF CAP3 2.2µF CAP4 CAP1-4 LED1-4 PWM1-4 SHDN LT3476 VADJ1-4 VC1-4
3476 TA03
1.05V
47nF
Package 38-Lead Plastic (5mm 7mm)
(Reference 05-08-1701)
5.00 0.10 SIDES) 0.75 0.05 0.00 0.05 3.15 0.10 SIDES) NOTCH 0.30 0.35 CHAMFER 0.40 ±0.10
7.00 0.10 SIDES)
5.15 0.10 SIDES)
0.40 ±0.10 0.25 0.05 0.50 0.115
BOTTOM VIEW-EXPOSED
(UH) 0205
NOTE: DRAWING CONFORMS JEDEC PACKAGE OUTLINE M0-220 VARIATION WHKD DRAWING SCALE DIMENSIONS MILLIMETERS
DIMENSIONS EXPOSED BOTTOM PACKAGE INCLUDE MOLD FLASH. MOLD FLASH, PRESENT, SHALL EXCEED 0.20mm SIDE EXPOSED SHALL SOLDER PLATED SHADED AREA ONLY REFERENCE LOCATION BOTTOM PACKAGE
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LT3476 TYPICAL APPLICATIO
PVIN 2.8V
4.7µH
2.2µF
LED1 LED2
LEDS
2.8V
PWM1-4 SHDN 2.2µF
RELATED PARTS
PART NUMBER DESCRIPTION LT1618 LTC3454 LTC3474 LT3475 LT3477 LT3479 1.5A, Constant-Current, 1.4MHz, Boost Converter Synchronous Buck-Boost Driver (ILED), 36V, 2MHz, Step-Down Driver Dual 1.5A (ILED), 36V, 2MHz, Step-Down Driver 42V, 3.5MHz Boost, Buck-Boost, Buck Driver Full-Featured DC/DC Converter with Soft-Start Inrush Current Protection COMMENTS VIN(MIN) VIN(MAX) 18V, VOUT(MAX) 36V, Dimming Analog/PWM, 1µA, MS10 Package VIN(MIN) 2.7V, VIN(MAX) 5.5V, VOUT(MAX) 5.5V, Dimming 4-Levels Adj, 1µA, DFN-10 Package VIN(MIN) VIN(MAX) 36V, VOUT(MAX) 13.5V, 400:1 True Color PWM, 1µA, TSSOP-16E Package VIN(MIN) 4.0V, VIN(MAX) 36V, VOUT(MAX) 13.5V, Dimming 3000:1 True Color PWM, 1µA, TSSOP-20E Package VIN(MIN) 2.5V, VIN(MAX) 25V, VOUT(MAX) 40V, Dimming Analog/PWM, 1µA, TSSOP-20E Packages VIN(MIN) 2.5V, VIN(MAX) 24V, VOUT(MAX) 40V, Dimming Analog/PWM, 1µA, TSSOP Packages
Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
1630 McCarthy Blvd., Milpitas, 95035-7417
www.linear.com
LINEAR TECHNOLOGY CORPORATION 2006
Quad Boost 100mA 8LED Driver
4.7µH 2.2µF 4.7µH 4.7µH CAP1 CAP2 2.2µF 2.2µF LED3 LED4 CAP3 CAP4 2.2µF 100mA 100mA 100mA 100mA 1.05V CAP1-4 LED1-4 PWM1-4 SHDN LT3476 VADJ1-4 VC1-4
3476 TA04
100k
47nF
3476f 0606 PRINTED

LT3476 High Current Quad Output Driver DESCRIPTIO LT®3476 quad ou

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